I heard that once the supernatant of cell culture is removed, the pellet can be kept in minus 20 fridge. However, I wonder if this can be done for long period of time. Also, please suggest if there can be alternative solutions to preserving bacterial pellet prior to lysis. Thank you all in advance.
It can be preserved for long in -80 oC. Just flash freeze by liquid nitrogen and keep in -80oC. But I dont think that -20oC is a good option for preserving cell pellets. Also ensure that pellet is media free.
I kept IPTG-induced E.coli at -200C for about 2 days and there were no problems. But for a long period I would use liquid nitrogen and -800C, as already was suggested by Subhajit Ghosh. But if your expressed protein is highly effected by proteases (I had such type of protein - it is digested in E. coli and in lysates of its native organism), I would mix the pellet with 10% glycerol before freezing. This, I think, will keep much of your cells alive so that proteases will not work.
Over expressing a protein can promote toxicity to the cells. There have been instances where I have kept the cells in -20C for three days with no problems in protein isolation. But if you plan to keep them for weeks before protein isolation, -80 would be the way to go. I've heard that some cultures can last upto a week in the -20, but that would be a stroke of luck.
In my experience it depends on the protein. It works most of the time, specially for proteins in inclusion bodies (I once saw someone store the cell paste from a 75 L fermentation for months at -20*C, divided into aliquots suitable for the scale of his chromatography setup. He had no problems). Then again, I agree with the posters above in that it would be best to use flash freezing and then storage at -80*C.
Yes. I also stored the pellet of IPTG-induced E.coli at -20 C for mounths and then I lysed it for protein purification without any problems.
I have stored IPTG-induced E. coli at -80 degrees before lysis for protein purification, both from inclusion bodies and soluble proteins. I did also try resuspending my pellet in lysis buffer before freezing, and that helped because the pellet is looser just after spinning than after freeze-thawing, although you would have to add fresh protease inhibitors to the lysis buffer after thawing. I would be a bit hesitant to do any of this at -20 degrees though. If that is all you have available, consider flash-freezing with liquid nitrogen before putting in -20, and try not to leave it at -20 for too long (maybe just overnight).
I have stored the Bacterial cell pellet at -20 for 3-4 months and observed no problem in protein purification.
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